From 33b27fc9a1bd5cb23dc85b0c08b7f6b529c2590b Mon Sep 17 00:00:00 2001
From: Curle <curle@gemwire.uk>
Date: Sat, 11 Mar 2023 07:57:03 +0000
Subject: [PATCH] Component API draft

---
 .../inc/component/EntityComponent.h           | 92 +++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 projs/shadow/shadow-engine/shadow-entity/inc/component/EntityComponent.h

diff --git a/projs/shadow/shadow-engine/shadow-entity/inc/component/EntityComponent.h b/projs/shadow/shadow-engine/shadow-entity/inc/component/EntityComponent.h
new file mode 100644
index 0000000..2e623fc
--- /dev/null
+++ b/projs/shadow/shadow-engine/shadow-entity/inc/component/EntityComponent.h
@@ -0,0 +1,92 @@
+#pragma once
+#include <cstdint>
+#include "id/ID.h"
+
+namespace SE {
+
+    /**
+     * A Component is a part of an Entity that stores and manages data.
+     * This data is held separately from the Entity that requests it.
+     *
+     * Components can be Spatial (ie. Position, Rotation).
+     * Components can also be Visual (ie. Mesh, Collider).
+     * Components are part of the larger Entity-Component-System architecture.
+     *
+     * Systems operate over these Components.
+     * Entities may have their own Systems, and each Scene has its own set of global Systems.
+     * Components may be registered to only one of these.
+     *
+     * EntityComponent classes are not singleton; new EntityComponent(..) is valid.
+     *
+     */
+    class EntityComponent {
+    public:
+
+        /**
+         * The Component's possible statuses.
+         */
+        enum class Status: uint8_t {
+            Unloaded,       // The component is not yet loaded.
+            Loading,        // The component is being loaded.
+            Loaded,         // The component is finished loading, but is not yet populated with data.
+            Failed,         // The component encountered an error while loading.
+            Initialized     // The component is finished loading, and is populated with data.
+        };
+
+        virtual ~EntityComponent();
+
+        // Get the ComponentID.
+        inline ComponentID const& GetID() const { return id; }
+        // Get the Name of this Component; guaranteed to be unique in a given entity.
+        inline std::string& GetName() { return name; }
+        // Get the Entity that owns this Component.
+        inline EntityID const& GetParent() const { return owner; }
+
+        inline Status GetStatus() const { return status; }
+        // Check Status
+        inline bool IsLoaded() const { return status == Status::Loaded; }
+        inline bool IsLoading() const { return status == Status::Loading; }
+        inline bool IsUnloaded() const { return status == Status::Unloaded; }
+        inline bool Failed() const { return status == Status::Failed; }
+        inline bool Initialized() const { return status == Status::Initialized; }
+
+        // Whether one instance of this Component is allowed per Entity
+        virtual bool IsSingleton() const { return false; }
+
+    protected:
+
+        EntityComponent() = default;
+        EntityComponent(std::string& name) : name(name) {}
+
+        // Load Component data. May perform background ops.
+        virtual void Load() = 0;
+        // Unload Component data. Must be blocking.
+        virtual void Unload() = 0;
+
+        // Check that everything went properly.
+        virtual void UpdateStatus() = 0;
+
+        // Update the status to Initialized. Must only be called if checks passed.
+        // The status must be Loaded.
+        virtual void Initialize() { status = Status::Initialized; }
+
+        // Prepare for unloading the Component. Must be called before the process begins.
+        // The status must be Initialized.
+        virtual void Close() { status == Status::Loaded; }
+
+    private:
+        // This Component's unique ID.
+        ComponentID id = ComponentID::Generate();
+        // The Entity that requested this Component.
+        EntityID owner;
+        // The name of the Component, for visualization
+        std::string name;
+        // The status of the Component
+        Status status = Status::Unloaded;
+
+        // Whether this Component is registered to the Entity's Local Systems.
+        bool localComponent = false;
+        // Whether this Component is registered to the Scene's Global Systems.
+        bool globalComponent = false;
+    };
+}
\ No newline at end of file